A new, stable dye-sensitized solar cell developed at Northwestern University promises to be a cheaper alternative to silicon cells (Photo: Martin L)

Solar power is up there as the quintessential clean energy and there’s a race worldwide to develop better solar cells to overcome current challenges related to cell efficiency, manufacturing costs, durability and materials, among other things. One of the latest developments in the sector comes from Northwestern University where researchers have developed a stable dye-sensitized solar cell that may one day prove cheaper than silicon-based cells.

The new cell design is a variation on the Grätzel cell (named after the Swiss chemist Michel Grätzel), a type of dye-sensitized solar cell that replaces silicon with the semiconductor titanium oxide, which is more abundant, cheaper and less toxic, further improving solar energy’s green credentials. However, there is a problem with the Grätzel design: its electrolyte is made of an organic liquid that leaks, threatening to corrode the cell. Northwestern University researchers have solved the problem by using a new material that solidifies, thus avoiding leaks and making the solid-state cell more stable. The material is a thin-film compound called CsSnI3, a combination of cesium, tin and iodine. It is added in liquid form to dye-coated nanoparticles and then it turns into a solid mass.

At 10.2 percent, the conversion rate leaves something to be desired when compared to silicon cells that can achieve around 20 percent, but it nearly matches the performance of a Grätzel cell, which reaches around 11 or 12 percent. The technology is projected to improve, however. "This is the first demonstration of an all solid-state dye-sensitized solar cell system that promises to exceed the performance of the Grätzel cell," researcher Robert P. H. Chang said. "Our work opens up the possibility of these materials becoming state of the art with much higher efficiencies than we’ve seen so far." The CsSnl3 compound can absorb more light than the dye used in Grätzel cells, increasing the cell's conversion potential.

But even if efficiency is not greatly increased, overall lower costs could make up for it and render the manufacturing of the cell, which is compatible with automated manufacturing, commercially viable and competitive with existing technologies. The researchers now plant to build a large array of solar cells to carry out further tests.

Details about the new solar cell were published in the journal Nature this week.